vitamin-k-1 and 2-phytyl-1-4-naphthoquinone

Δ⁹-tetrahydrocannabinol (THC), through its action on cannabinoid type-1 receptor (CB₁R), is known to activate dopamine (DA) neurotransmission. Functional evidence of a direct antagonistic interaction between CB₁R and DA D₂-receptors (D₂R) suggests that D₂R may be an important target for the modulation of DA neurotransmission by THC. The current study evaluated, in rodents, the effects of chronic exposure to THC (1 mg/kg/day; 21 days) on D₂R and D₃R availabilities using the D₂R-prefering antagonist and the D₃R-preferring agonist radiotracers [¹⁸F]fallypride and [³H]-(+)-PHNO, respectively. At 24 h after the last THC dose, D₂R and D₃R densities were significantly increased in midbrain. In caudate/putamen (CPu), THC exposure was associated with increased densities of D₂R with no change in D₂R mRNA expression, whereas in nucleus accumbens (NAcc) both D₃R binding and mRNA levels were upregulated. These receptor changes, which were completely reversed in CPu but only partially reversed in NAcc and midbrain at 1 week after THC cessation, correlated with an increased functionality of D₂/₃R in vivo, based on findings of increased locomotor suppressive effect of a presynaptic dose and enhanced locomotor activation produced by a postsynaptic dose of quinpirole. Concomitantly, the observations of a decreased gene expression of tyrosine hydroxylase in midbrain together with a blunted psychomotor response to amphetamine concurred to indicate a diminished presynaptic DA function following THC. These findings indicate that the early period following THC treatment cessation is associated with altered presynaptic D₂/₃R controlling DA synthesis and release in midbrain, with the concurrent development of postsynaptic D₂/₃R supersensitivity in NAcc and CPu. Such D₂/₃R neuroadaptations may contribute to the reinforcing and habit-forming properties of THC.

Topics: Amphetamine; Analysis of Variance; Animals; Basal Ganglia; Benzamides; Dopamine Agonists; Dopamine Antagonists; Dopamine Uptake Inhibitors; Dose-Response Relationship, Drug; Dronabinol; Drug Interactions; Fluorodeoxyglucose F18; Gene Expression Regulation; Locomotion; Male; Nucleus Accumbens; Positron-Emission Tomography; Protein Binding; Psychotropic Drugs; Quinpirole; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D2; RNA, Messenger; Tritium; Vitamin K 1

In a recent human [(11)C]-(+)-PHNO positron emission tomography study, olanzapine, clozapine, and risperidone occupied D2 receptors in striatum (STR), but, despite their similar in vitro D2 and D3 affinities, failed to occupy D3 receptors in globus pallidus. This study had two aims: (1) to characterize the regional D2/D3 pharmacology of in vitro and ex vivo [(3)H]-(+)-PHNO binding sites in rat brain and (2) to compare, using [(3)H]-(+)-PHNO autoradiography, the ex vivo and in vitro pharmacology of olanzapine, clozapine, risperidone, and haloperidol. Using the D3-selective drug SB277011, we found that ex vivo and in vitro [(3)H]-(+)-PHNO binding in STR is exclusively due to D2, whereas that in cerebellar lobes 9 and 10 is exclusively due to D3. Surprisingly, the D3 contribution to [(3)H]-(+)-PHNO binding in the islands of Calleja, ventral pallidum, substantia nigra, and nucleus accumbens was greater ex vivo than in vitro. Ex vivo, systemically administered olanzapine, risperidone, and haloperidol, at doses occupying approximately 80% D2, did not occupy D3 receptors. Clozapine, which also occupied approximately 80% of D2 receptors ex vivo, occupied a smaller percentage of D3 receptors than predicted by its in vitro pharmacology. Across brain regions, ex vivo occupancy by antipsychotics was inversely related to the D3 contribution to [(3)H]-(+)-PHNO binding. In contrast, in vitro occupancy was similar across brain regions, independent of the regional D3 contribution. These data indicate that at clinically relevant doses, olanzapine, clozapine, risperidone, and haloperidol are D2-selective ex vivo. This unforeseen finding suggests that their clinical effects cannot be attributed to D3 receptor blockade.

Topics: Animals; Antipsychotic Agents; Autoradiography; Benzodiazepines; Clozapine; Dose-Response Relationship, Drug; Haloperidol; Humans; In Vitro Techniques; Male; Olanzapine; Protein Binding; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D2; Risperidone; Tritium; Vitamin K 1

The finding that the mGlu2/3 metabotropic glutamate receptor agonist, LY404039, improves clinical symptoms in schizophrenia warrants a search for a possible interaction between mGlu2/3 receptors and dopamine D2 receptors. Here, this topic is examined in striatal tissue of mice lacking either mGlu2 or mGlu3 receptor. Such mice are known to be behaviorally supersensitive to dopamine receptor agonists. Therefore, to determine the basis of this dopamine supersensitivity, the proportion of dopamine D2(High) receptors was measured in the striata of mGlu2 and mGlu3 receptor knockout mice. The proportion of D2(High) receptors was found to be elevated by 220% in the striata of both knockouts. To measure the functional dopamine supersensitivity, the D2 agonist (+)PHNO was used to stimulate the incorporation of GTP-gamma-S in the striatal homogenates in the presence of drugs that blocked the dopamine D1, D3, and D5 receptors. Compared with control striata, the mGlu2 receptor knockout tissues were 67-fold more sensitive to (+)PHNO, while the mGlu3 receptor knockout tissues were 17-fold more sensitive. These data suggest that group II mGlu receptors-mGlu2 receptors in particular-may normally regulate D2 receptors by reducing the proportion of high-affinity D2 receptors in membranes. Such regulation may contribute to the antipsychotic action of mGlu2/3 receptor agonists.

Topics: Animals; Binding, Competitive; Corpus Striatum; Domperidone; Dopamine; Dopamine Agonists; Dopamine Antagonists; Dose-Response Relationship, Drug; Guanosine 5'-O-(3-Thiotriphosphate); Mice; Mice, Knockout; Oxazines; Protein Binding; Receptors, AMPA; Receptors, Dopamine D2; Receptors, Metabotropic Glutamate; Vitamin K 1

Although the glutamate agonist LY 404,039 has been used to treat schizophrenia, its closest congener LY 379,268 has an affinity for both glutamate and dopamine (DA) D2(High) receptors. Considering that all antipsychotics act on dopamine receptors, and considering that another laboratory reported that LY 379,268 did not have any affinity for the D2(High) receptor, it was necessary to examine whether such glutamate agonists have an affinity for D2 and D3 dopamine receptors in vitro. The present data show that 50-200 nM LY 379,268 inhibited the binding of [(3)H]domperidone and [(3)H](+)PHNO to cloned dopamine D2 receptors consistently and reproducibly by 16% with dissociation constants of 2.1 and 2.5 nM at D2(High), respectively. In addition, LY 379,268 inhibited the binding of [(3)H]domperidone and [(3)H](+)PHNO to cloned dopamine D3 receptors with dissociation constants of 130 and 10 nM, respectively. LY 379,268 also inhibited the binding of [(3)H]domperidone to rat striata with a dissociation constant of 22 nM, predicting a clinical antipsychotic dose of 80-100 mg/day. LY 379,268 appears to act as an agonist at D2(High) and as an antagonist at D3, because guanine nucleotide eliminated the competition at D2(High) but had no effect on the competition at D3. The findings indicate that this type of glutamate agonist, LY 379,268, has a significant affinity for D2(High) and D3 receptors.

Topics: Amino Acids; Animals; Binding, Competitive; Brain; Bridged Bicyclo Compounds, Heterocyclic; CHO Cells; Cricetinae; Cricetulus; Domperidone; Dopamine Antagonists; Dose-Response Relationship, Drug; Excitatory Amino Acid Agonists; Humans; Male; Protein Binding; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D2; Receptors, Dopamine D3; Transfection; Tritium; Vitamin K 1

Dopaminergic stabilizers are recognized as compounds that can either enhance or antagonize dopamine (DA)-dependent behaviors depending on the prevailing dopaminergic tone. The dopaminergic stabilizer ASP2314 is being tested clinically and has been reported to have antipsychotic effects in a clinical trial as an add on medication. To elucidate the mechanisms of action of this dopaminergic stabilizer, its potency on the functional dopamine D2(High) receptors was examined. In competition with D2 receptors selectively labeled by [3H]domperidone, ASP2314 had a dissociation constant, Ki(High), of 1.62 microM for D2(High) in human cloned D2Long receptors and 0.83 muM for rat homogenized striata. Using the D2 agonist ligand [3H](+)-4-propyl-3,4,4a,5,6,10b-hexahydro-2H-naphtho[1,2-b][1,4]oxazin-9-ol ((+)PHNO), ASP2314 had a high-affinity Ki of 32 nM for D2(High) for rat homogenized striata. ASP2314 stimulated the incorporation of [35S]GTP-gamma-S into rat striata by 50% at 43 nM, and into the cloned D2Long membranes by 50% at 3.2 microM (compared to 100% stimulation by 10 microM dopamine). With similar concentrations of ASP2314 inhibiting the binding of ligands at D2(High) and stimulating [35S]GTP-gamma-S incorporation, the data indicate that the dopaminergic stabilizing action of ASP2314 may be related to the selectivity for the D2(high) state of the D2 receptor.

Topics: Animals; Binding, Competitive; Brain; CHO Cells; Cloning, Molecular; Cricetinae; Cricetulus; Dopamine; Dose-Response Relationship, Drug; Drug Interactions; Guanosine 5'-O-(3-Thiotriphosphate); Male; Piperidines; Protein Binding; Radioisotopes; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D2; Transfection; Vitamin K 1

The glutamate agonist LY404,039 has been used to treat schizophrenia. Because all currently used antipsychotics act on dopamine receptors, it was decided to examine whether this glutamate agonist also had an affinity for dopamine D2 receptors in vitro. The present data show that LY404,039 inhibited the binding of [3H]domperidone and [3H]+PHNO by 15.5 +/- 1.5% to the high-affinity state, D2(High), of cloned dopamine D2(Long) receptors and rat striatal tissue with dissociation constants of between 8.2 and 12.6 nM. This high-affinity component of LY404,039 on the binding of [3H]domperidone was inhibited by the presence of guanine nucleotide, indicating an agonist action of the drug at D2(High). LY404,039 also stimulated the incorporation of [35S]GTP-gamma-S into D2(Long) receptors (EC50% = 80 +/- 15 nM) over the same range of concentrations as occurred for the inhibition of [3H]domperidone by LY404,039 at D2(High) (IC50%(High) = 50 +/- 10 nM). A possible clinical antipsychotic action of LY404,039 may depend on the combined stimulation of glutamate receptors and a partial dopamine agonist action that would interfere with neurotransmission at D2(High) receptors.

Topics: Animals; Binding, Competitive; Bridged Bicyclo Compounds, Heterocyclic; CHO Cells; Corpus Striatum; Cricetinae; Cricetulus; Cyclic S-Oxides; Domperidone; Dopamine Antagonists; Excitatory Amino Acid Agonists; Guanosine 5'-O-(3-Thiotriphosphate); Humans; Protein Binding; Radioisotopes; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D2; Transfection; Vitamin K 1

A phylloquinone molecule (2-methyl-3-phytyl-1,4-naphthoquinone) occupies the A1 binding site in photosystem I. Previously, we have obtained A1(-)/A1 FTIR difference spectra using labeled and unlabeled photosystem I particles and proposed assignments for many of the bands in the spectra [Sivakumar, V., Wang, R., and Hastings, G. (2005) Biochemistry 44, 1880-1893]. In particular, we suggested that a negative/positive band at 1654/1495 cm(-1) in A1(-)/A1 FTIR DS is due to a C=O/C-:O mode of the neutral/anionic phylloquinone, respectively. To test this hypothesis, we have obtained A1(-)/A1 FTIR DS for menG mutant PS I particles. In menG mutant PS I, phylloquinone in the A1 binding site is replaced with an analogue in which the methyl group at position 2 of the quinone ring is replaced with a hydrogen atom (2-phytyl-1,4-naphthoquinone). In A1(-)/A1 FTIR DS obtained using menG mutant PS I particles, we find that the 1654/1495 cm(-1) bands are upshifted by approximately 6 cm(-1). To test if such upshifts are likely for C=O/C-:O modes of neutral/anionic phylloquinone, we have used density functional theory to calculate the "anion minus neutral" infrared difference spectra for both phylloquinone and its methyl-less analogue. We have also undertaken calculations in which the C4=O carbonyl group of phylloquinone and its methyl-less analogue are hydrogen bonded (to a water or leucine molecule). We find that, irrespective of the hydrogen bonding state of the C4=O group, the C=O/C-:O modes of neutral/reduced phylloquinone are indeed expected to be upshifted by at least 6 cm(-1) upon replacement of the methyl group at position 2 with hydrogen. The calculations also suggest that certain C=C/C-:C modes of neutral/reduced phylloquinone do not shift upon replacement of the methyl group. On the basis of these calculated results, we suggest which bands in the A1(-)/A1 FTIR DS may be associated with C=C/C-:C modes of neutral/reduced phylloquinone, respectively.

Topics: Binding Sites; Computer Simulation; Models, Molecular; Photosystem I Protein Complex; Spectroscopy, Fourier Transform Infrared; Vitamin K 1